Move with arrows. Click a new box to move that box instead.
http://willhostforfood.com/files3/39399 ... Player.cap
It doesn't use a custom control scheme, but the important part isn't whether it's using behaviors, but rather which object has the "active" variable turned on. You could just add a "value('active') is equal to 1" condition to all of your movement code.
As far as which of many different sprites are being controlled, that's what Families are for
(And yeah, I realize it could probably be made much simpler, I just sort of threw it together.)